The present invention pertains to an apparatus for removing condensate from a high speed, steam heated rotary cylindrical roll and, more particularly, to an apparatus which provides positive pumped removal of condensate.
Rotary cylindrical rolls are used in a wide variety of material treating applications. In one particularly well known use, webs of material to be treated are wrapped around a heated rotary roll which transmits heat to the web. Steam is the most commonly used heating fluid and steam heated rolls are well known in the art. Typically, steam is supplied to and condensate water removed from the interior of the roll via axial bores in the roll shaft and utilizing joints for steam supply and siphon tubes for condensate withdrawal. The steam may be supplied to the entire open interior of the roll or may be directed to axial passages formed in the interior cylindrical wall of the roll. Condensate removal may be effected with a non-rotating siphon tube having an inlet positioned near the interior of the roll shell at the lowermost point of roll rotation. Alternately, the roll may be provided with radially extending condensate removal tubes which extend from the roll shell inwardly to a common condensate outlet in the roll shaft.
In co-pending and commonly assigned U.S. patent application Ser. No. 08/932,332, filed Sep. 17, 1997, an apparatus is disclosed for removing condensate from a steam heated roll operating either at rimming speed, when the condensate is evenly distributed by centrifugal force around the inside of the roll shell, or at low speed when gravity causes the condensate to pool at the bottom of the roll shell. The disclosure of that application is incorporated herein by, reference. In the apparatus disclosed therein, steam is supplied to a series of circumferentially spaced, generally parallel and axially extending open ended steam tubes in the cylindrical outer wall of the roll. Steam is supplied to the tubes and steam pressure differential moves the condensate out of the opposite tube ends and radially inwardly to the axis of the roll where the condensate is discharged through a connection to the roll shaft. With heated roll diameters up to about 48 inches (1,220 mm), and handling webs having a line speed up to about 1,300 feet per minute, the corresponding rotational speed is 100 rpm. The centrifugal force causing rimming at this speed may be overcome by system steam pressure differential sufficient to allow the condensate to be removed.
However, in certain industries, much larger heated rolls operating at much greater speeds are utilized. For example, in the paper industry, a web drying roll may be made to a diameter of 72 inches (about 1,830 mm), rotated to handle a web speed of 6,000 feet per minute, requiring a roll speed of about 320 rpm. At this high rotational speed, the centrifugal force on the condensate is so great that condensate cannot be efficiently removed under the influence of system steam pressure alone. The prior art discloses complex arrangements for removing condensate from high speed rolls using elaborate nozzle arrangements positioned in close proximity to the thin layers of condensate created by rimming. At high roll speeds, external suction pumps are required to assist in the removal of condensate, but rotational speeds may be so high that even these pumps are ineffective. Therefore, the detrimental insulating effects of condensate and the difficulty of effectively removing condensate remain a problem.